In the field of radiation sensors and sensor systems, prior sensors either are integrating devices which are not capable of suppressing background radiation, or they have low quantum efficiency at the wavelength high-power pulsed lasers are available.
In order to overcome the deficiencies of the sensors, some prior sensor systems use two sensors. One is for sensing passive radiating targets, and the other, for laser illuminated targets. The disadvantage of those systems is that their optics must be common to both sensors in order to reduce boresight misalignment, and the optical paths must be separated with beam splitters, which reduces the optical transmission.
Prior dual-mode systems, systems which can be operated in both active and passive modes, use a single sensor to both search for, and acquire, the target or object of interest. Thereby, a great deal more sophistication and higher data rate is required than is necessary for tracking alone.
Other prior dual-mode systems in which the active system includes a laser, use the passive sensor to confirm lock-on in the active mode. The disadvantage in those systems is that laser tracking, with its bang-bang operation, causes the scene on the passive sensor to be smeared.